Ben Foster has kept six clean sheets since moving to Birmingham City in May for £6m. Photograph: Andrew Matthews/EMPICS Sport

Ben Foster says he has no regrets about leaving Manchester United in the summer and believes joining Birmingham City has helped him to recapture his best form. The England international, who will come up against his former team-mates at St Andrew's tonight, is relieved to have escaped the pressure at United, which he described as a "cut-throat" environment where two dropped points represented "the end of the world".

Expectations are nothing like as great at Birmingham and Foster has thrived away from the Old Trafford spotlight. He has impressed with some outstanding displays, earning a recall to Fabio Capello's squad after the disappointment of missing out on the World Cup. He is playing well enough to suggest Sir Alex Ferguson might have been a little rash to dispense with a player he once described as "England's goalkeeper for the next 10 years".

With the United manager back in the market for a No1 goalkeeper in the wake of Edwin van der Sar's decision to retire, Foster could be forgiven for wondering whether he should have stayed on for another season. But that is far from his mind. "I'm loving it [at Birmingham], I've never enjoyed my football more. I don't wish I'd stuck around at all," said Foster, who cost Birmingham £6m in May.

"I don't really keep up to date with what's going on [at United]. I look out for results but nothing more than that. I wouldn't go back [on the decision to leave]. I had a loan spell at Watford [2005‑2007] and had a great time but this is the best time I've had. I think I'm back to my best, I feel good and I'm enjoying my football. I'm playing week in, week out and I've been given that chance and it's working out."

Foster was given an opportunity at United at the start of last season, when Van der Sar was sidelined, but his confidence was shattered after he made mistakes against Chelsea, Arsenal, Manchester City and Sunderland by the first week of October. He made only one more Premier League appearance for United.

"It's just a bit more relaxed at Birmingham than it was at United," said Foster. "A club like United is cut-throat, win at all costs, whereas here you know you're not going to win every game but the players that we've got, we battle for 90 minutes and don't give someone a second breath. There is more pressure at United, without a doubt. Even if we drew it was the end of the world, two points dropped, regardless if we got back into it in the last minute."

Foster has kept six clean sheets since moving to Birmingham, with Chelsea and Manchester City among those that have been frustrated by the former Stoke City goalkeeper. He says it is up to him to "show United what they're missing", although he points out that it is much easier to attract praise for his performances in a Birmingham jersey than it was in any of the 23 appearances he made for United.

"At United, if you're playing you are expected to be one of the best players in the world in your position. It's as simple as that. Playing well is what you should do anyway. So perhaps here you do get more credit for playing well. I see match reports and see 'unbelievable save from Foster' when it was just routine. I'm like: 'Don't get carried away. It wasn't that good.'"